1. Field of the Invention
The invention is in the field of LED-based emergency lighting. Generally, LED-based emergency lighting systems, equipment and methodologies according to exemplary embodiments of the present invention utilize AC-DC switch mode power conversion technology, NiMH battery technology, and emergency lighting lamps that use high power white LEDs as the emergency lighting source.
2. Discussion of the Background of the Invention
For many years commercial two lamp emergency lighting unit designs have primarily been based around three key design elements to achieve costs that were acceptable in the marketplace while delivering reasonable levels of performance lighting the path of egress in emergency situations. These three design elements in most emergency lighting units include (1) Valve Regulated Lead Acid (VRLA) batteries, (2) incandescent DC lamps, and (3) 60 Hz transformer based voltage controlled chargers. These elements combine to provide typical entry level emergency lighting units that are widely used and stocked by electrical distributors to meet the basic emergency lighting needs.
The choice of these traditional design elements for emergency lighting units has typically been dictated by a narrow range of DC light sources that could light the path of egress from battery power after a loss of AC power to the unit. Incandescent lamps for many years were the only sources that could offer the amount of light required for the application at a reasonable price point. Traditional entry level emergency lighting units typically use two 6V 5.4 W incandescent lamps. Because these incandescent light sources have relatively low efficacy levels, the batteries required to power them for the 90 minute run times mandated by NFPA 101 life safety codes were heavy and bulky VRLA types. The typical battery size for most entry level emergency lighting units is the 6V 4 Ah VRLA battery. This battery size is convenient because it matches the voltage rating of the lamp and can deliver code mandated run times with two 6V 5.4 W incandescent lamp sources. The 6V system is also widely used because it allows the use of a simple relay to transfer the battery power to the lamps during emergency conditions when AC power is lost to a building.
Because the battery sizes of the traditional emergency lighting unit are relatively large the chargers used to keep the batteries in a fully charged state also have to be sized to charge these larger batteries. Typical entry level emergency lighting units employ a 60 Hz magnetic step down transformer and a voltage controlled charging regulator to provide a well regulated dc voltage source needed to maintain the batteries in a fully charged state. Thus, one of the problems for traditional emergency lighting units is the need for relatively large and heavy batteries and battery chargers.
With recent advances in white high power LED lighting technology LEDs have reached luminous output levels where they can provide light levels equivalent to the traditional lamps technologies at much lower power levels. Because of the higher level of efficacy for the LED source, much lower AC input power requirements can be achieved for general purpose lighting fixtures. This significant energy usage reduction for the LED source has driven rapid adoption of the LED as a light source in general purpose, normally on, lighting fixtures in recent years. While the advances in LED lighting technology have made the LED a viable replacement lighting source in general purpose lighting fixtures the costs associated with the LED light source are significantly higher than more established traditional light sources. The disadvantageous high costs are likewise associated with conventional emergency lighting units attempting to use LED light sources.